Aqueous ink for development of concealed images

ABSTRACT

A SYSTEM FOR PREPARING OF COPY CONTAINING CONCEALED IMAGES AND A MARKING MATERIAL FOR THE DEVELOPMENT OF SAME IN WHICH THE COMPONENTS COMPRISE A RECEIVING MATERIAL IN THE FORM OF STARCH OR POLYVINYL ALCOHOL, AN IODIDE WHICH IS OXIDIZABLE TO IODINE, AND AN OXIDIZING AGENT FOR OXIDIZING THE IODIDE IN WHICH THE OXIDIZING AGENT IS CONTAINED IN THE IMAGING MATERIAL TO PRODUCE THE CONCEALED IMAGE, THE IODINE IS CONTAINED IN THE MARKING MATERIAL FOR THE DEVELOPMENT OF THE IMAGE AND THE STARCH OF POLYVINYL ALCOHOL ARE CONTAINED IN THE COPY SHEET, THE PRINTING MATERIAL OR THE MARKING MATERIAL WHEREBY, WHEN THE MARKING MATERIAL IS APPLIED TO THE CONCEALED IMAGE, THE OXIDIZING AGENT OXIDIZES THE IODIDE TO RELEASE IODINE FOR PRODUCING AN INTENSE COLOR WITH THE STARCH OR POLYVINYL ALCOHOL AND IN WHICH THE PRINTING PROCESS IS ADAPTED TO CONVENTIONAL PRINTING SYSTEMS.

Jan.29,1974 1 S HE ER 3,788,863

AQUEOUS INK FOR DEVELOPMENT OF CONCEALFD IMAGES Original Filed Sept. 5,1968 FIG. I

I I I 0 Fza v IN VZNTOP RAM/0N0 62/4505? United States Patent U.S. Cl.10621 2 Claims ABSTRACT OF THE DISCLOSURE A system for the preparing ofcopy containing concealed images and a marking material for thedevelopment of same in which the components comprise a receivingmaterial in the form of starch or polyvinyl alcohol, an iodide which isoxidizable to iodine, and an oxidizing agent for oxidizing the iodide inwhich the oxidizing agent is contained in the imaging material toproduce the concealed image, the iodine is contained in the markingmaterial for the development of the image and the starch of polyvinylalcohol are contained in the copy sheet, the printing material or themarking material whereby, when the marking material is applied to theconcealed image, the oxidizing agent oxidizes the iodide to releaseiodine for producing an intense color with the starch or polyvinylalcohol and in which the printing process is adapted to conventionalprinting systems.

This is a division of the copending application Ser. No. 757,067, filedSept. 3, 1968, and entitled Printed Sheets Containing Concealed Imagesand Method and Materials for Preparation and Visual Development of Same.

This invention relates to materials, elements and methods used ininformational systems and testing systems embodying concealed or thecombination of concealed and visible images and in the preparation anddevelopment thereof.

A system of the type described finds utilization in the field that isreferred to as concealed image development where use is made thereof inself-instructional material, self-examination and multiple choicetechniques for learning, testing and the like. In self-instructionalmaterial, only the image corresponding to the correct answer containsone or more components for visual development when properly marked witha writing substance embodying an additional component or componentsrequired for color development to indicate when the correct answer hasbeen marked.

In self-examination and in multiple choice systems, the

same concepts are embodied. For further utilization of these concepts inconcealed image development, reference can be made to U.S. Pat. No.3,451,143.

It is an object of this invention to provide a three component systemfor use in the preparation and development of concealed images and it isa related object to provide materials and elements for use in thepractice of same, which give wider latitude in the distribution ofcomponents and in the utilization thereof in learning or instructionalsystems, which gives more rapid visible image development and increasedcolor intensity in the developed image, and which provides elementshaving greater shelf life and stability under widely varying conditionsof heat and humidity, and which are capable of use in conventionalprinting processes for preparation of multiple copies containing theconcealed image alone or in combinations with visible images.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustra- "ice tion, but not oflimitation, an embodiment of the invention is shown in the accompanyingdrawing in which FIG. 1 is a sectional elevational view showing thearrangement of elements in the imaging of a spirit master;

FIG. 2 is a schematic view, partially in section, of the imaged master;and 1 FIG. 3 is a schematic view, partially in section, showing theproduction of printed copies from the imaged spirit master of FIG. 2.

The three component system of this invention comprises an iodide capableof oxidation to release iodine, an oxidizing agent capable of oxidizingthe iodide to yield iodine, and a receiving material which reacts withthe released iodine to form an intensely colored product.

The invention will be described with reference to the distribution ofthe three components of the system in the elements of a spiritduplicating copy process for the production of multiple copiescontaining a concealed image for subsequent development and a markingmaterial with which the copy sheets can be marked for visibledevelopment of the image. It will be understood that the threecomponents can be otherwise distributed in elements for producingmultiple copies by other printing processes, such as by stencilduplication, lithographic printing, letterpress printing, flexographicprinting, gravure printing, screen printing and the like, or by handstamp, as will hereinafter be defined.

As the iodide, it is preferred to make use of ammonium or an alkalimetal iodide, such as potassium iodide, sodium iodide and the like.Since the iodide is embodied in the marking material, use can be made ofcolored iodide salts capable of being oxidized to release iodine.

As the component with which the released iodine reacts to produce avisible image, use is made of a material that is invisible in the copysheet and, for such purpose, it is preferred to make use of a starch orpolyvinyl alcohol or mixtures thereof, which is invisible when embodiedin the desired amounts in the copy sheet.

As the oxidizing agent, it is desirable to make use of material which isinvisible in the copy sheet to enable use in defining the invisibleimage. For this purpose, it is preferred to make use of a soluble saltof copper, such as the chloride, nitrate, sulphate, acetate, lactate,benzoate, or stearate of copper. Use can be made of a double salt CuCl-KCl and cupric ammonium chloride. Instead, use can be made of suchother oxidizing agents as copper-mbenzene disulfonate and the like.

Excellent results have been secured from the use of an invisibleoxidizing material referred to as positive halogen oxidizing agent inwhich the halogen is attached to nitrogen and which can be representedby trichloromelamine, N-chlorosuccinimide, N-bromosuccinimide,N-chlorophthalimide, monobromantin, diodantin, dibromomethyl ethylhydantoin, dichloromethyl ethyl hydantoin, N-bromogluterimide,N-chloroglutar-imide, -N- haloaminotriazines, Dichloramine B (WyandotteChemical Co.), and Halane (Wyandotte Chemical Co.).

Copper chloride and related salts are highly hygroscopic or deliquescentsuch that difiiculties are sometimes encountered in use under highhumidity conditions of the type prevailing in the southern regions ofthe United States and on hot and humid summer days. The use of suchcopper salts can be greatly improved in their stability by thecombination with the copper salts of the type previously described.Excellent results are also secured by combination of the copper saltswith an amine such as piperidine, piperazine, phenylenediamine,tallowamine, trichloromelamine, triisopropanolamine, melamine and thelike.

For the preparation of copy, in accordance with the preferred practiceof this invention, the oxidizing component is embodied in the transfercoating of the transfer sheet for use in imaging a spirit master. Thestarch or polyvinyl alcohol is embodied in the copy sheet. Since theiodide is subject to slow oxidation in air with corresponding release ofiodine and color, it is undesirable to embody the iodide either in thecopy sheet or the printing material forming the invisible image appliedto the copy sheet. Thus the iodide is preferably embodied as a componentin the marking fluid with which the imaged copy sheet is marked todevelop the visible image when applied to engage the invisible image. Inanother ramification, the receiving material, such as starch and/orpolyvinyl alcohol, can be incorporated with the iodide in the markingmaterial.

Having described the basic concepts of this invention, illustration willnow be made by way of an example of the distribution of the elements inthe preparation of copy by spirit duplication and in the use thereof todevelop the invisible image.

Example 1 Copy paper In the preparation of the copy paper, it will besufficient if the copy paper is formulated to contain at least 0.1% byweight starch and/or polyvinyl alcohol, although it is preferred to makeuse thereof in an amount within the range of 0.5% to 5% by weight of thecopy paper. The starch or polyvinyl alcohol can be incorporated foruniform distribution throughout the copy paper by formulation as acomponent dissolved or dispersed in the slurry or finish of which thepaper is formed by conventional paper making technique. In the preferredpractice, the starch and/or polyvinyl alcohol is incorporated intoalready formed paper by impregnation and preferably by coating the paperwith a solution containing from 3-10% by weight starch or polyvinylalcohol in aqueous medium whereby the starch or polyvinyl alcohol isconcentrated on the surface of the paper where it is more available forreaction with the released iodine.

Example 2 Transfer sheet The transfer sheet embodying the oxidizingagent in the transfer coating can be prepared in the conventional mannerfor the preparation of transfer sheets in spirit duplication. Thefollowing is a typical formulation for a transfer coating in which theoxidizing material is incorporated:

4 Example 2-d Parts by weight Copper-m-benzene disulfonate l5Trichloromelamiue 15 Dioctyl phthalate 8 Ethyl cellulose 2.5 Toluene 40The materials are ball milled and then coated onto paper at the rate of10 to 20 pounds per 3,000 square feet of surface area, calculated on adry weight basis.

As the oxidizing agent in Examples 2 and 2-b, the copper chloride can bereplaced by equivalent amounts of copper nitrate, copper sulphate,copper acetate, copper lactate, copper benzoate, copper-m-benzenedisulfonate, CuClyKCl with the copper salt being present preferably inan amount within the range of 5 to 25 parts by weight. Instead of copperchloride, use can be made of cupric ammonium chloride. Instead of thetrichloromelamine in Example 2-d, use can be made of other positivehalogen such as N-chlorosuccinimide, N-bromosuccinimide, N-chlorophthalimide, monobromantin, diodantin, dibromomethyl ethylhydantoin, dichloromethyl ethyl hydantoin, N bromoglutarimide, Nchloroglutarimide, N haloaminotriazines, Dichlorarnine B (WyandotteChemical Co.), and Halane (Wyandotte Chemical Co.), with the positivehalogen being present preferably in an amount within the range of 15 to30 parts by weight.

Instead of the oxidizing agent in Examples 2 to 2-d, use can be made ofa mixture of a copper salt and a positive halogen in the ratio of 1 partby weight copper salt to 0.2 to 2 parts by weight of the positivehalogen and preferably within the range of 1 part by weight of thecopper salt to 0.5 to 2 parts by weight of the positive halogen. Insteadof making use of a copper salt in Example 2, use can be made of amixture of copper salts and an amine such as piperidine, piperazine,phenylenediamine, tallowamine, trichloromelamine, triisopropanolamine,melamine and the like, in the ratio of 1 part by weight copper salt to0.1 to 2 parts by weight of the amine and preferably 1 part by weight ofthe copper salt to 0.4 to 2 parts by weight of the amine.

Example 3 Marking material The following is a typical formulation of afluid marking material:

Parts by weight Iodide 1-10 Water 99-90 Example 3-a Percent by weightPotassium iodide 2 Water 97 Dyestufl 1 Instead of locating the markingiodide in a fluid system, it can be formulated into a wax crayon, pencilor the like element which can be used for marking.

Example 4 Preparation of copy by spirit duplication With reference nowto FIG. 1, the transfer sheet 2 is positioned with the transfer coating4 of Example 2 in surface contact with the duplicating surface of aspirit master 6. The spirit master is imaged by transfer of coating fromthe transfer sheet to the master surface in the normal manner inresponse to impact or pressure from a die, typewriter key, stylus orpencil, or in response to a heat pattern generated by infrared radiationof an infrared ray absorbing original positioned in surface contact withthe transfer sheet. The master may be additionally imaged by aconventional spirit master to provide a master imaged in part with aspirit and alcohol soluble dyestuff from an imaged master having avisible image 8 and an invisible image 10.

For the production of copy, as illustrated in FIG. 2, the imaged master6 is mounted on the cylinder of a conventional spirit duplicatingmachine and copy sheets 12, wetted on one surface 14 with a spiritfluid, are brought into surface contact with the imaged surface of themaster whereby some of the imaging materials are leached from the imageportions of the master for transfer to the copy sheets to produce copiescontaining an invisible image 16 formed of the oxidizing agent andvisible images 18, if the master had an imaged portion containing adyestuff, or if the copy sheets originally contained a visible image.

Thereafter the copy sheets can be used as a piece of instructionalmaterial or test material distributed for use. When in marking the sheetwith the marking fluid of Example 3, the marking fluid is applied to anon-imaged portion of the sheet, only a color introduced by the markingmaterial to indicate the place that has been marked will show. When themarking material is applied to an invisible image, the iodide in themarking material is immediately oxidized by the oxidizing agent in theinvisible image to release iodine and the iodine stains or reacts withthe starch to provide a visible image of high color intensity toindicate that the marking material has been applied to a portion of thecopy sheet containing the visible image.

Having described the basic concepts of this invention, reference willnow be made to the distribution of components for use in other printingprocesses for producing multiple copies of the sheet printed with theinvisible and visible image.

In the lithographic printing process, the oxidizing material will beformulated as a component of the lithographic ink which preferentiallywets the imaged portions of the lithographic surface as distinguishedfrom the non-imaged hydrophilic portions which are previously wet withWater.

In stencil duplication, the oxidizing agent is formulated in the stencilfluid that is forced through the stencil openings onto the copy sheetsto form the invisible image thereon.

In letterpress printing, the oxidizing material will be embodied in thefluid with which the letters of the plate are wet for imprinting thecopy sheets.

In gravure printing, the oxidizing material will be formulated into thefluid that is retained in the wells etched into the surface of the platefor transfer to copy paper brought into contact therewith.

In a hand stamp or in silk screen printing, the fluid ink would beformulated to contain the oxidizing agent.

In each of these other processes, the iodide would still be limited toformulation into the marking material with which the printed sheet ismarked and by polyvinyl alcohol or starch to be embodied with theoxidizing agent in the printing fluid or with the iodide in the markingmaterial and preferably in the paper on which the copy is produced.

The following example is typical of a printing ink embodying theoxidizing agent for use in a hand stamp:

Example 5 Dioxin preservative (Sindar Corp.) drops 4 Ammonium alum"gram" .25 Gum arabic grams..... 9.00

6 Penford Gum-200 do 3.50 Formalin gram .75 Sodium stearate do 1.00Water grams 84.00 Glycerine 36.5 n-Butanol ml 10.00 Trichloromelaminegram 0.725 Copper chloride do 0.725

The Penford Gum (starch) is heated and stirred until dissolved or formedinto a colloidal dispersion which is then combined with the remainder ofthe ingredients and dispersed as by means of a ball mill, colloid millor the The prepared ink composition can be applied to impression or copypaper with a rubber stamp, a silk screen printing process, a jetprinting process, or by letterpress. The dried ink images are invisibleand development can be accomplished by treating the appropriate areaswith a 2% aqueous solution of potassium iodide.

In the above formulations, copper-m-benzene disulfonate can besubstituted for the trichloromelamine and either the trichloromelamineor copper chloride can be used solely as the oxidizing agent incorresponding amounts. Polyvinyl alcohol or carboxymethylcellulose canbe substituted for the Penford gum. The copper chloride ortrichloromelamine can be replaced with other copper salts or with apositive halogen oxidizing agent or combination thereof in amounts toconstitute 0.5 to 10% by weight of the ink.

In the event that some slight color is present in the materials formingthe latent image, this can be concealed by the technique of making useof tinted copy or impression paper, preferably of the same tint as theimage so as better to conceal the image.

It will be apparent from the foregoing that we have provided a new andimproved system for use of concealed images in educational, testing andthe like programs whereby an invisible image can be made highly visiblewhen properly marked with an iodide containing material.

It will be understood that changes may be made in the details ofconstruction, formulation and operation without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. An ink for development of concealed images formed of a soluble coppersalt and a receiving material selected from the group consisting ofstarch, polyvinyl alcohol and mixtures thereof in which the inkconsisting essentially of water containing a soluble iodide selectedfrom the group consisting of ammonium and an alkali metal iodide capableof oxidation by the copper salt to release iodine which reacts with thestarch to produce a colored reaction product and a dye or pigment havingvisible color value for visual display of the portions wet with the ink.

2. A marking material as claimed in claim 1 in which the iodide ispresent in a soluble state in an amount within the range of l10% byweight.

References Cited UNITED STATES PATENTS 2,229,091 1/ 1941 Kline 106-20 X3,632,364 1/1972 Thomas 106-21 X 3,363,336 1/ 1968 Skinner 117-36.8 X

OTHER REFERENCES Warth: The Chemistry and Technology of Waxes, 2nd ed.,Reinhold Publishing Corp, New York, 1956, pp. 34, 568, 356371.

JOAN B. EVANS, Primary Examiner US. Cl. X.R. 106-22, 23, 25

UNITED STATES PATENT OFFICE I 7 CERTIFICATE OF CORRECTION Patent3,788,863 Dated January 29, 1974 Ra 0nd I, cheuer Inventor(s) y W I Itis certified that error appears in the above-ider ltified patent andthat saidLetters Patent are hereby corrected as shown below:

- Assignee: A, B. Dick Company Niles, Illinois Signed and sealed this9th day of July 197 I.

(SEAL) Attest: McCOY M.GIBSON,JR. c; MARSHALL DANN Attesting Officer ICommissioner of Patents .uscoMM-Dc eoan-Poo FORM Po-wso (10-69)

